Suchergebnisse

La cuprosklodovskite est triclinique ; ses paramètres sont :
a = 7.04 À, b = 9.18 Â, c = 6.66 Â, a = 109°14', ß = 90°0', y = 108°22'.
Les cristaux, aciculaires, sont allongés suivant l'axe a [100] et portent les faces
{001}, {011}, {010}, {111}, {110}, {120}, {210}.
Les macles sont fréquentes, soit avec axe de macie [100] et plan de jonction (010), soit avec plan de macie (210).
L'orientation optique est précisée, ainsi que les indices de réfraction et l'angle des axes optiques.

La jachimovite appartient au système triclinique, groupe spatial Pl. Ses paramètres, déterminés par Mélon et Dejace, sont a = 7,04 Å, b = 9,18 Å, c = 6,66 Å, ɑ = 109°14', β = 90°00' et γ = 108°22'. Z = 1[CuH2(UO2SiO4)2 . 5H2O].
La méthode d'investigation était la diffraction des RX par un monocristal. L'interprétation de la fonction de Patterson, suivie de synthèses de Fourier normales et des différences, montre que le minéral présente une structure en feuillets parallèles, constitués par les ions (UO2SiO4)[formula] unis entre eux par les cations Cu++.

The author has considered three quadratic forms (i) ƒ = Gaβduaduβ (ii) θ = μaβduaduβ and (iii) Φ — ξaβduaduβ. With the help of these quadratic forms ten distinct families of ruled surfaces have been obtained. The intersection of these ruled surfaces with the surface of reference yields interesting results. Also, some particular cases have been studied.

The author shows that the thermodynamics of the plane capillary layer described with the aid of a Gibbs dividing surface may not allways be applied to any dividing surface. The use of an arbitrary dividing surface is correct only when the chemical potentials satisfy to two conditions. These two conditions are satisfied in the case of equilibrium, but out of equilibrium, the use of an arbitrary dividing surface involves a loss of generality.

The equations for the evolution in time of irreversible processes are written in a variational form in some important cases (thermal conductibility, chemical reactions). The stationnary non equilibrium states are shown to be characterized by a minimum of a quadratic function of the velocities or rates of the irreversible processes. In the neighbourhood of equilibrium, this function reduces to the entropy production per unit time in accordance with a theorem derived previously by the author. The variational principle introduced here which may be called «the principle of the least velocities », plays a role somewhat similar to the Gauss principle of the «least constraints » in classical mechanics.